1. Field of the Invention
The present invention relates to a control valve driven by a stepping motor, and in particular, to a control valve that can be miniaturized while required pressure resistance and a structure robust against vibrations (vibration resistance) are being maintained.
2. Description of the Related Art
An automotive air conditioner has a refrigeration cycle including a compressor, an external heat exchanger, an evaporator, and an internal heat exchanger, etc., and the functions of the external heat exchanger are switched to each other between a heating operation and a cooling operation. During the heating operation, the external heat exchanger functions as an evaporator. In the case, the internal heat exchanger radiates heat while a refrigerant is circulating the refrigeration cycle, the heat heating the air in the interior of a vehicle. On the other hand, during the cooling operation, the external heat exchanger functions as a condenser. In the case, the refrigerant condensed in the external heat exchanger evaporates in the evaporator, the latent heat of the evaporation cooling the air therein. At the time, the air is also dehumidified.
When a plurality of evaporators function in accordance with an operating state of a refrigeration cycle in this way, it is necessary to adjust a ratio of flow rates of a refrigerant flowing through the respective evaporators. The same is true with the case where a plurality of condensers function. Accordingly, a control valve whose opening degree can be electrically adjusted is sometimes provided at a specific position in a refrigerant circulation passage, and in general, an electromagnetic valve driven by a solenoid, by which large drive force can be obtained at a relatively low cost, is often used. When it is necessary to precisely control an opening degree of a valve, however, it is desirable to use a control valve driven by a stepping motor, as frequently seen in residential air conditioners.
Because an automotive air conditioner is greatly influenced by vibrations occurring during vehicle running, an environment in which the air conditioner is installed is not stable, unlike a residential air conditioner. In addition, both a valve element that forms a control valve and a drive mechanism that drives the valve element are arranged in a refrigerant passage where the pressure of a refrigerant acts. Accordingly, the drive mechanism of the control valve, including a stepping motor, is arranged in a housing having pressure resistance in order to surely prevent the refrigerant from leaking out. In addition, the housing is firmly fixed to the body of the control valve in order to secure a structure robust against vibrations (a structure having high vibration resistance), the structure being sufficiently able to withstand the vibrations received from a vehicle (see, for example, Patent Documents 1 and 2).